Dual aperture zoom camera with video support and switching / non-switching dynamic control

ABSTRACT

A dual-aperture zoom digital camera operable in both still and video modes. The camera includes Wide and Tele imaging sections with respective lens/sensor combinations and image signal processors and a camera controller operatively coupled to the Wide and Tele imaging sections. The Wide and Tele imaging sections provide respective image data. The controller is configured to output, in a zoom-in operation between a lower zoom factor (ZF) value and a higher ZF value, a zoom video output image that includes only Wide image data or only Tele image data, depending on whether a no-switching criterion is fulfilled or not.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/324,720 filed Jan. 8, 2017 (now allowed), which was a 371 applicationfrom international patent application PCT/IB2016/053803 filed Jun. 26,2016, and is related to and claims priority from U.S. Provisional PatentApplication No. 62/204,667 filed Aug. 13, 2015 which is expresslyincorporated herein by reference in its entirety.

FIELD

Embodiments disclosed herein relate in general to digital cameras and inparticular to zoom digital cameras with video capabilities.

BACKGROUND

Digital camera modules are currently being incorporated into a varietyof host devices. Such host devices include cellular telephones, personaldata assistants (PDAs), computers, and so forth. Consumer demand fordigital camera modules in host devices continues to grow.

Host device manufacturers prefer digital camera modules to be small, sothat they can be incorporated into the host device without increasingits overall size. Further, there is an increasing demand for suchcameras to have higher-performance characteristics. One suchcharacteristic possessed by many higher-performance cameras (e.g.,standalone digital still cameras) is the ability to vary the focallength of the camera to increase and decrease the magnification of theimage. This ability, typically accomplished with a zoom lens, is knownas optical zooming. “Zoom” is commonly understood as a capability toprovide different magnifications of the same scene and/or object bychanging the focal length of an optical system, with a higher level ofzoom associated with greater magnification and a lower level of zoomassociated with lower magnification. Optical zooming is typicallyaccomplished by mechanically moving lens elements relative to eachother. Such zoom lenses are typically more expensive, larger and lessreliable than fixed focal length lenses. An alternative approach forapproximating the zoom effect is achieved with what is known as digitalzooming. With digital zooming, instead of varying the focal length ofthe lens, a processor in the camera crops the image and interpolatesbetween the pixels of the captured image to create a magnified butlower-resolution image.

Attempts to use multi-aperture imaging systems to approximate the effectof a zoom lens are known. A multi-aperture imaging system (implementedfor example in a digital camera) includes a plurality of opticalsub-systems (also referred to as “cameras”). Each camera includes one ormore lenses and/or other optical elements which define an aperture suchthat received electro-magnetic radiation is imaged by the opticalsub-system and a resulting image is directed towards a two-dimensional(2D) pixelated image sensor region. The image sensor (or simply“sensor”) region is configured to receive the image and to generate aset of image data based on the image. The digital camera may be alignedto receive electromagnetic radiation associated with scenery having agiven set of one or more objects. The set of image data may berepresented as digital image data, as well known in the art. Hereinafterin this description, “image” “image data” and “digital image data” maybe used interchangeably. Also, “object” and “scene” may be usedinterchangeably. As used herein, the term “object” is an entity in thereal world imaged to a point or pixel in the image.

Multi-aperture imaging systems and associated methods are described forexample in US Patent Publications No. 2008/0030592, 2010/0277619 and2011/0064327. In US 2008/0030592, two sensors are operatedsimultaneously to capture an image imaged through an associated lens. Asensor and its associated lens form a lens/sensor combination. The twolenses have different focal lengths. Thus, even though each lens/sensorcombination is aligned to look in the same direction, each combinationcaptures an image of the same subject but with two different fields ofview (FOV). One sensor is commonly called “Wide” and the other “Tele”.Each sensor provides a separate image, referred to respectively as“Wide” (or “W”) and “Tele” (or “T”) images. A W-image reflects a widerFOV and has lower resolution than the T-image. The images are thenstitched (fused) together to form a composite (“fused”) image. In thecomposite image, the central portion is formed by the relativelyhigher-resolution image taken by the lens/sensor combination with thelonger focal length, and the peripheral portion is formed by aperipheral portion of the relatively lower-resolution image taken by thelens/sensor combination with the shorter focal length. The user selectsa desired amount of zoom and the composite image is used to interpolatevalues from the chosen amount of zoom to provide a respective zoomimage. The solution offered by US 2008/0030592 requires, in video mode,very large processing resources in addition to high frame raterequirements and high power consumption (since both cameras are fullyoperational).

US 2010/0277619 teaches a camera with two lens/sensor combinations, thetwo lenses having different focal lengths, so that the image from one ofthe combinations has a FOV approximately 2-3 times greater than theimage from the other combination. As a user of the camera requests agiven amount of zoom, the zoomed image is provided from the lens/sensorcombination having a FOV that is next larger than the requested FOV.Thus, if the requested FOV is less than the smaller FOV combination, thezoomed image is created from the image captured by that combination,using cropping and interpolation if necessary. Similarly, if therequested FOV is greater than the smaller FOV combination, the zoomedimage is created from the image captured by the other combination, usingcropping and interpolation if necessary. The solution offered by US2010/0277619 leads to parallax artifacts when moving to the Tele camerain video mode.

In both US 2008/0030592 and US 2010/0277619, different focal lengthsystems cause matching Tele and Wide FOVs to be exposed at differenttimes using CMOS sensors. This degrades the overall image quality.Different optical F numbers (“F#”) cause image intensity differences.Working with such a dual sensor system requires double bandwidthsupport, i.e. additional wires from the sensors to the following HWcomponent. Neither US 2008/0030592 nor US 2010/0277619 deal withregistration errors.

US 2011/0064327 discloses multi-aperture imaging systems and methods forimage data fusion that include providing first and second sets of imagedata corresponding to an imaged first and second scene respectively. Thescenes overlap at least partially in an overlap region, defining a firstcollection of overlap image data as part of the first set of image data,and a second collection of overlap image data as part of the second setof image data. The second collection of overlap image data isrepresented as a plurality of image data cameras such that each of thecameras is based on at least one characteristic of the secondcollection, and each camera spans the overlap region. A fused set ofimage data is produced by an image processor, by modifying the firstcollection of overlap image data based on at least a selected one of,but less than all of, the image data cameras. The systems and methodsdisclosed in this application deal solely with fused still images.

None of the known art references provide a thin (e.g. fitting in acell-phone) dual-aperture zoom digital camera with fixed focal lengthlenses, the camera configured to operate in both still mode and videomode to provide still and video images, wherein the camera configurationdoes not use any fusion to provide a continuous, smooth zoom in videomode.

Therefore there is a need for, and it would be advantageous to have thindigital cameras with optical zoom operating in both video and still modethat do not suffer from commonly encountered problems and disadvantages,some of which are listed above.

SUMMARY

Embodiments disclosed herein teach the use of dual-aperture (alsoreferred to as dual-lens or two-sensor) optical zoom digital cameras.The cameras include two cameras, a Wide camera and a Tele camera, eachcamera including a fixed focal length lens, an image sensor and an imagesignal processor (ISP). The Tele camera is the higher zoom camera andthe Wide camera is the lower zoom camera. In some embodiments, thethickness/effective focal length (EFL) ratio of the Tele lens is smallerthan about 1. The image sensor may include two separate 2D pixelatedsensors or a single pixelated sensor divided into at least two areas.The digital camera can be operated in both still and video modes. Invideo mode, optical zoom is achieved “without fusion”, by, in someembodiments, switching between the W and T images to shortencomputational time requirements, thus enabling high video rate. To avoiddiscontinuities in video mode, the switching includes applyingadditional processing blocks, which include in some embodiments imagescaling and shifting. In some embodiments, when a no-switching criterionis fulfilled, optical zoom is achieved in video mode without switching.

As used herein, the term “video” refers to any camera output thatcaptures motion by a series of pictures (images), as opposed to “stillmode” that friezes motion. Examples of “video” in cellphones andsmartphones include “video mode” or “preview mode”.

In order to reach optical zoom capabilities, a different magnificationimage of the same scene is captured (grabbed) by each camera, resultingin FOV overlap between the two cameras. Processing is applied on the twoimages to fuse and output one fused image in still mode. The fused imageis processed according to a user zoom factor request. As part of thefusion procedure, up-sampling may be applied on one or both of thegrabbed images to scale it to the image grabbed by the Tele camera or toa scale defined by the user. The fusion or up-sampling may be applied toonly some of the pixels of a sensor. Down-sampling can be performed aswell if the output resolution is smaller than the sensor resolution.

The cameras and associated methods disclosed herein address and correctmany of the problems and disadvantages of known dual-aperture opticalzoom digital cameras. They provide an overall zoom solution that refersto all aspects: optics, algorithmic processing and system hardware (HW).

In a dual-aperture camera image plane, as seen by each camera (andrespective image sensor), a given object will be shifted and havedifferent perspective (shape). This is referred to as point-of-view(POV). The system output image can have the shape and position of eithercamera image or the shape or position of a combination thereof. If theoutput image retains the Wide image shape then it has the Wideperspective POV. If it retains the Wide camera position then it has theWide position POV. The same applies for Tele images position andperspective. As used in this description, the perspective POV may be ofthe Wide or Tele cameras, while the position POV may shift continuouslybetween the Wide and Tele cameras. In fused images, it is possible toregister Tele image pixels to a matching pixel set within the Wide imagepixels, in which case the output image will retain the Wide POV (“Widefusion”). Alternatively, it is possible to register Wide image pixels toa matching pixel set within the Tele image pixels, in which case theoutput image will retain the Tele POV (“Tele fusion”). It is alsopossible to perform the registration after either camera image isshifted, in which case the output image will retain the respective Wideor Tele perspective POV.

In an exemplary embodiment, there is provided a zoom digital cameracomprising a Wide imaging section that includes a fixed focal lengthWide lens with a Wide FOV and a Wide sensor, the Wide imaging sectionoperative to provide Wide image data of an object or scene, a Teleimaging section that includes a fixed focal length Tele lens with a TeleFOV that is narrower than the Wide FOV and a Tele sensor, the Teleimaging section operative to provide Tele image data of the object orscene, and a camera controller operatively coupled to the Wide and Teleimaging sections, the camera controller configured to evaluate ano-switching criterion determined by inputs from both Wide and Teleimage data, and, if the no-switching criterion is fulfilled, to output azoom video output image that includes only Wide image data in a zoom-inoperation between a lower zoom factor (ZF) value and a higher ZF value.

In an exemplary embodiment there is provided a method for obtaining zoomimages of an object or scene using a digital camera, comprising thesteps of providing in the digital camera a Wide imaging section having aWide lens with a Wide FOV and a Wide sensor, a Tele imaging sectionhaving a Tele lens with a Tele FOV that is narrower than the Wide FOVand a Tele sensor, and a camera controller operatively coupled to theWide and Tele imaging sections, and configuring the camera controller toevaluate a no-switching criterion determined by inputs from both Wideand Tele image data, and, if the no-switching criterion is fulfilled, tooutput a zoom video output image that includes only Wide image data in azoom-in operation between a lower ZF value and a higher ZF value.

In some exemplary embodiments, the no-switching criterion includes ashift between the Wide and Tele images calculated by globalregistration, the shift being greater than a first threshold.

In some exemplary embodiments, the no-switching criterion includes adisparity range calculated by global registration, the disparity rangebeing greater than a second threshold.

In some exemplary embodiments, the no-switching criterion includes aneffective resolution of the Tele image being lower than an effectiveresolution of the Wide image.

In some exemplary embodiments, the no-switching criterion includes anumber of corresponding features in the Wide and Tele images beingsmaller than a third threshold.

In some exemplary embodiments, the no-switching criterion includes amajority of objects imaged in an overlap area of the Wide and Teleimages being calculated to be closer to the camera than a firstthreshold distance.

In some exemplary embodiments, the no-switching criterion includes someobjects imaged in an overlap area of the Wide and Tele images beingcalculated to be closer than a second threshold distance while otherobjects imaged in the overlap area of the Wide and Tele images beingcalculated to be farther than a third distance threshold.

In some exemplary embodiments, the camera controller includes a usercontrol module for receiving user inputs and a sensor control module forconfiguring each sensor to acquire the Wide and Tele image data based onthe user inputs.

In some exemplary embodiments, the user inputs include a zoom factor, acamera mode and a region of interest.

In some exemplary embodiments, the Tele lens includes a ratio of totaltrack length (TTL)/effective focal length (EFL) smaller than 1. For adefinition of TTL and EFL see e,g. co-assigned US published patentapplication No. 20150244942.

In some exemplary embodiments, if the no-switching criterion is notfulfilled, the camera controller is further configured to output videooutput images with a smooth transition when switching between the lowerZF value and the higher ZF value or vice versa, wherein at the lower ZFvalue the output image is determined by the Wide sensor, and wherein atthe higher ZF value the output image is determined by the Tele sensor.

In some exemplary embodiments, the camera controller is furtherconfigured to combine in still mode, at a predefined range of ZF values,at least some of the Wide and Tele image data to provide a fused outputimage of the object or scene from a particular point of view.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples of embodiments disclosed herein are describedbelow with reference to figures attached hereto that are listedfollowing this paragraph. Identical structures, elements or parts thatappear in more than one figure are generally labeled with a same numeralin all the figures in which they appear. The drawings and descriptionsare meant to illuminate and clarify embodiments disclosed herein, andshould not be considered limiting in any way.

FIG. 1A shows schematically a block diagram illustrating an exemplarydual-aperture zoom imaging system disclosed herein;

FIG. 1B is a schematic mechanical diagram of the dual-aperture zoomimaging system of FIG. 1A:

FIG. 2 shows an example of a Wide sensor, a Tele sensor and theirrespective FOVs;

FIG. 3A shows an embodiment of an exemplary method disclosed herein foracquiring a zoom image in video/preview mode;

FIG. 3B shows exemplary feature points in an object;

FIG. 3C shows schematically a known rectification process;

FIG. 4 shows a graph illustrating an effective resolution zoom factor.

DETAILED DESCRIPTION Definitions

Sharpness score: the gradients (dx, dy) of the image are compared(through subtraction) to the gradients of its low pass filtered version.A higher difference indicates a sharper original image. The result ofthis comparison is normalized with respect to the average variations(for example, sum of absolute gradients) of the original image, toobtain an absolute sharpness score.

Edge score: for each image, the edges are found (for example, usingCanny edge detection) and the average intensity of gradients along themis calculated, for example, by calculating the magnitude of gradients(dx, dy) for each edge pixel, summing the results and dividing by thetotal number of edge pixels. The result is the edge score.

Effective resolution score: this score is calculated only in a region ofinterest (ROI) and provides a good indication of the effectiveresolution level in the image. As used herein, “ROI” is a user-definedsub-region of the image that may be exemplarily 4% or less of the imagearea. The effective resolution score can be derived from a combinationof the sharpness scores and edge scores for each image, for example bynormalizing both to be between [0, 1] and by taking their average.

FIG. 1A shows schematically a block diagram illustrating an exemplaryembodiment of a dual-aperture zoom imaging system (also referred tosimply as “dual-camera” or “dual-aperture camera”) disclosed herein andnumbered 100. Dual-aperture camera 100 comprises a Wide imaging section(“Wide camera”) that includes a Wide lens block 102, a Wide image sensor104 and a Wide image processor 106. Dual-aperture camera 100 furthercomprises a Tele imaging section (“Tele camera”) that includes a Telelens block 108, a Tele image sensor 110 and a Tele image processor 112.The image sensors may be physically separate or may be part of a singlelarger image sensor. The Wide sensor pixel size can be equal to ordifferent from the Tele sensor pixel size. Dual-aperture camera 100further comprises a camera fusion processing core (also referred to as“controller”) 114 that includes a sensor control module 116, a usercontrol module 118, a video processing module 126 and a captureprocessing module 128, all operationally coupled to sensor control block110. User control module 118 comprises an operational mode function 120,a ROI function 122 and a zoom factor (ZF) function 124.

Sensor control module 116 is connected to the two (Wide and Tele)cameras and to the user control module 118 and used to choose, accordingto the zoom factor, which of the sensors is operational and to controlthe exposure mechanism and the sensor readout. Mode choice function 120is used for choosing capture/video modes. ROI function 122 is used tochoose a region of interest. The ROI is the region on which both camerasare focused on. Zoom factor function 124 is used to choose a zoomfactor. Video processing module 126 is connected to mode choice function120 and used for video processing. It is configurable to evaluate ano-switching criterion determined by inputs from both Wide and Teleimage data and to make a decision regarding video output. Specifically,upon evaluation of a no-switching criterion, if the no-switchingcriterion is fulfilled, module 126 is configurable to output a zoomvideo output image that includes only Wide image data in a zoom-inoperation between a lower zoom factor (ZF) value and a higher ZF value.If the no-switching criterion is not fulfilled, module 126 isconfigurable to combine in still mode, at a predefined range of ZFvalues, at least some of the Wide and Tele image data to provide a fusedoutput image of the object or scene from a particular point of view.Still processing module 128 is connected to the mode choice function 120and used for high image quality still mode images. The video processingmodule is applied when the user desires to shoot in video mode. Thecapture processing module is applied when the user wishes to shoot stillpictures.

FIG. 1B is a schematic mechanical diagram of the dual-aperture zoomimaging system of FIG. 1A. Exemplary dimensions: Wide lens TTL=4.2 mmand EFL=3.5 mm; Tele lens TTL=6 mm and EFL=7 mm; both Wide and Telesensors ⅓ inch; external dimensions of Wide and Tele cameras: width (w)and length (1)=8.5 mm and height (h)=6.8 mm; distance “d” between cameracenters=10 mm.

Following is a detailed description and examples of different methods ofuse of dual-aperture camera 100.

Still Mode Operation/Function

In still camera mode, the obtained image is fused from informationobtained by both cameras at all zoom levels, see FIG. 2, which shows aWide sensor 202 and a Tele sensor 204 and their respective FOVs.Exemplarily, as shown, the Tele sensor FOV is half the Wide sensor FOV.The still camera mode processing includes two stages: the first stageincludes setting HW settings and configuration, where a first objectiveis to control the sensors in such a way that matching FOVs in bothimages (Tele and Wide) are scanned at the same time, a second objectiveis to control the relative exposures according to the lens properties,and a third objective is to minimize the required bandwidth from bothsensors for the ISPs. The second stage includes image processing thatfuses the Wide and the Tele images to achieve optical zoom, improves SNRand provides wide dynamic range.

FIG. 3A shows image line numbers vs. time for an image section capturedby CMOS sensors. A fused image is obtained by line (row) scans of eachimage. To prevent matching FOVs in both sensors to be scanned atdifferent times, a particular configuration is applied by the cameracontroller on both image sensors while keeping the same frame rate. Thedifference in FOV between the sensors determines the relationshipbetween the rolling shutter time and the vertical blanking time for eachsensor.

Video Mode Operation/Function

Smooth Transition

When a dual-aperture camera switches the camera output between camerasor points of view, a user will normally see a “jump” (discontinuous)image change. However, a change in the zoom factor for the same cameraand POV is viewed as a continuous change. A “smooth transition” (ST) isa transition between cameras or POVs that minimizes the jump effect.This may include matching the position, scale, brightness and color ofthe output image before and after the transition. However, an entireimage position matching between the camera outputs is in many casesimpossible, because parallax causes the position shift to be dependenton the object distance. Therefore, in a smooth transition as disclosedherein, the position matching is achieved only in the ROI region whilescale brightness and color are matched for the entire output image area.

Zoom-in and Zoom-Out in Video Mode

In video mode, sensor oversampling is used to enable continuous andsmooth zoom experience. Processing is applied to eliminate the changesin the image during crossover from one camera to the other. Zoom from 1to Z_(switch) is performed using the Wide sensor only. From Z_(switch)and on, it is performed mainly by the Tele sensor. To prevent “jumps”(roughness in the image), switching to the Tele image is done using azoom factor which is a bit higher (Z_(switch)+ΔZoom) than Z_(switch).ΔZoom is determined according to the system's properties and isdifferent for cases where zoom-in is applied and cases where zoom-out isapplied (ΔZoom_(in), ΔZoom_(out)). This is done to prevent residualjumps artifacts to be visible at a certain zoom factor. The switchingbetween sensors, for an increasing zoom and for decreasing zoom, is doneon a different zoom factor.

The zoom video mode operation includes two stages: (1) sensor controland configuration and (2) image processing. In the range from 1 toZ_(switch), only the Wide sensor is operational, hence, power can besupplied only to this sensor. Similar conditions hold for a Wide AFmechanism. From Z_(switch)+ΔZoom to Z_(max) only the Tele sensor isoperational, hence, power is supplied only to this sensor. Similarly,only the Tele sensor is operational and power is supplied only to it fora Tele AF mechanism. Another option is that the Tele sensor isoperational and the Wide sensor is working in low frame rate. FromZ_(switch) to Z_(switch)+ΔZoom, both sensors are operational.

Zoom-in:

at low ZF up to slightly above ZF_(T) (the zoom factor that enablesswitching between Wide and Tele outputs) the output image is thedigitally zoomed, unchanged Wide camera output. ZF_(T) is defined asfollows:ZF_(T)=Tan(FOV_(Wide))/Tan(FOV_(Tele))where Tan refers to “tangent”, while FOV_(Wide) and FOV_(Tele) referrespectively to the Wide and Tele lens fields of view (in degrees). Asused herein, the FOV is measured from the center axis to the corner ofthe sensor (i.e. half the angle of the normal definition). Switchingcannot take place below ZF_(T) and it can above it.

In some embodiments for the up-transfer ZF, as disclosed in co-inventedand co-owned U.S. Pat. No. 9,185,291, the output is a transformed Telecamera output, where the transformation is performed by a globalregistration (GR) algorithm to achieve smooth transition. As used herein“global registration” refers to an action for which the inputs are theWide and Tele images. The Wide image is cropped to display the same FOVas the Tele image. The Tele image is passed through a low pass filter(LPF) and resized to make its appearance as close as possible to theWide image (lower resolution and same pixel count). The outputs of GRare corresponding feature point pairs in the images along with theirdisparities, and parameters for differences between the images, i.e.shift and scale. As used herein, “feature point” refers to a point suchas points 10 a-d in FIG. 3B and refers to a point (pixel) of interest onan object in an image. For purposes set forth in this description, afeature point should be reproducible and invariant to changes in imagescale, noise and illumination. Such points usually lie on corners orother high-contrast regions of the object.

Stages of Global Registration

In some exemplary embodiments, global registration may be performed asfollows:

1. Find interest points (features) in each image separately by filteringit with, exemplarily, a Difference of Gaussians filter, and findinglocal extrema on the resulting image.

2. Find feature correspondences (features in both images that describethe same point in space) in a “matching” process. These are alsoreferred to as “feature pairs”, “correspondence pairs” or “matchingpairs”. This is done by comparing each feature point from one (Tele orWide) image (referred to hereinafter as “image 1”) to all feature pointsin that region from the other (respectively Wide or Tele) image(referred to hereinafter as “image 2”). The features are compared onlywithin their group of minima/maxima, using patch normalizedcross-correlation. As used herein, “patch” refers to a group ofneighboring pixels around an origin pixel.3. The normalized cross correlation of two image patches t(x,y) andf(x,y) is

$\frac{1}{n}{\sum\limits_{x,y}\frac{\left( {{f\left( {x,y} \right)} - \overset{\_}{f}} \right)\left( {{t\left( {x,y} \right)} - \overset{\_}{t}} \right)}{\sigma_{f}\sigma_{t}}}$where n is the number of pixels in both patches, f is the average of fand σ_(f) is the standard deviation of f. A match for a feature pointfrom image 1 is only confirmed if its correlation score is much higher(for example, x1.2) than the next-best matching feature from image 2.4. Find the disparity between each pair of corresponding features (alsoreferred to as “matching pair”) by subtracting their x and y coordinatevalues.5. Filter bad matching points:

a. Following the matching process, matches that include feature pointsfrom image 2 that were matched to more than one feature from image 1 arediscarded.

b. Matching pairs whose disparity is inconsistent with the othermatching pairs are discarded. For example, if there is one correspondingpair which whose disparity is lower or higher than the others by 20pixels.

6. The localization accuracy for matched points from image 2 is refinedby calculating a correlation of neighboring pixel patches from image 2with the target patch (the patch around the current pixel (of thecurrent matching pair) from image 1, modeling the results as a parabolaand finding its maximum.7. Rotation and fine scale differences are calculated between the twoimages according to the matching points (for example, by subtracting thecenter of mass from each set of points, i.e. the part of the matchingpoints belonging to either the Wide or the Tele image, and solving aleast squares problem).8. After compensating for these differences, since the images wererectified, the disparity in the Y axis should be close to 0. Matchingpoints that do not fit this criterion are discarded. A knownrectification process is illustrated in FIG. 3C.9. Finally, the remaining matching points are considered true and thedisparities for them are calculated. A weighted average of the disparityis taken as the shift between both images. The maximum differencebetween disparity values is taken as the disparity range.10. At various stages during GR, if there are not enoughfeature/matching points remaining, the GR is stopped and returns afailure flag.

In addition, it is possible to find range calibration to therectification process by finding the shiftI=shift for objects atinfinity and defining shiftD=shift-shiftI and disparityD=disparity-shiftI. We then calculate

${{{object}\mspace{14mu}{distance}} = \frac{{focalLength} \cdot {baseline}}{{disparityD} \cdot {pixelSize}}},$where “baseline” is the distance between cameras.

Returning now to the Zoom-in process, in some embodiments, for higher ZFthan the up-transfer ZF the output is the transformed Tele cameraoutput, digitally zoomed. However, in other embodiments for higher ZFthan the up-transfer ZF there will be no switching from the Wide to theTele camera output, i.e. the output will be from the Wide camera,digitally zoomed. This “no switching” process is described next.

No Switching

Switching from the Wide camera output to the transformed Tele cameraoutput will be performed unless some special condition (criterion),determined based on inputs obtained from the two camera images, occurs.In other words, switching will not be performed only if at least one ofthe following no-switching criteria is fulfilled:

1. if the shift calculated by GR is greater than a first threshold, forexample 50 pixels.

2. if the disparity range calculated by GR is greater than a secondthreshold, for example 20 pixels, because in this case there is noglobal shift correction that will suppress movement/jump for all objectsdistances (smooth transition is impossible for all objects).3. if the effective resolution score of the Tele image is lower thanthat of the Wide image. In this case, there is no point in performingthe transition because no value (i.e. resolution) is gained. Smoothtransition is possible but undesirable.4. if the GR fails, i.e. if the number of matching pairs found is lessthan a third threshold, for example 20 matching pairs.5. if, for example, that are imaged onto the overlap area are calculatedto be closer than a first threshold distance, for example 30 cm, becausethis can result in a large image shift to obtain ST.6. if some objects (for example two objects) that are imaged in theoverlap area are calculated to be closer than a second thresholddistance, for example 50 cm, while other objects (for example twoobjects) are calculated to be farther than a third threshold distancefor example 10 m. The reason is that the shift between an objectposition in the Wide and Tele cameras is object distance dependent,where the closer the objects the larger the shift, so an imagecontaining significantly close and far objects cannot be matched bysimple transformation (shift scale) to be similar and thus provide STbetween cameras.

Zoom-Out:

At high ZF down to slightly below Z_(FT), the output image is thedigitally zoomed transformed Tele camera output. For the down-transferZF, the output is a shifted Wide camera output, where the Wide shiftcorrection is performed by the GR algorithm to achieve smoothtransition, i.e. with no jump in the ROI region. For lower (than thedown-transfer) ZF, the output is basically the down-transfer ZF outputdigitally zoomed but with gradually smaller Wide shift correction, untilfor ZF=1 the output is the unchanged Wide camera output.

Note that if a no-switching criterion is not fulfilled, then the camerawill output without fusion continuous zoom video mode output images ofthe object or scene, each output image having a respective outputresolution, the video output images being provided with a smoothtransition when switching between the lower ZF value and the higher ZFvalue or vice versa, wherein at the lower ZF value the output resolutionis determined by the Wide sensor, and wherein at the higher ZF value theoutput resolution is determined by the Tele sensor.

FIG. 3A shows an embodiment of a method disclosed herein for acquiring azoom image in video/preview mode for 3 different zoom factor (ZF)ranges: (a) ZF range=1:Z_(switch); (b) ZFrange=Z_(switch):Z_(switch)+ΔZoom_(in): and (c) Zoom factorrange=Z_(switch)+ΔZoom_(in):Z_(max). The description is with referenceto a graph of effective resolution vs. zoom factor (FIG. 4). In step302, sensor control module 116 chooses (directs) the sensor (Wide, Teleor both) to be operational. Specifically, if the ZF range=1:Z_(switch),module 116 directs the Wide sensor to be operational and the Tele sensorto be non-operational. If the ZF range isZ_(switch):Z_(switch)+ΔZoom_(in), module 116 directs both sensors to beoperational and the zoom image is generated from the Wide sensor. If theZF range is Z_(switch)+ΔZoom_(in):Z_(max), module 116 directs the Widesensor to be non-operational and the Tele sensor to be operational.After the sensor choice in step 302, all following actions are performedin video processing core 126. Optionally, in step 304, color balance iscalculated if two images are provided by the two sensors. Optionallyyet, in step 306, the calculated color balance is applied in one of theimages (depending on the zoom factor). Further optionally, in step 308,registration is performed between the Wide and Tele images to output atransformation coefficient. The transformation coefficient can be usedto set an AF position in step 310. In step 312, an output of any ofsteps 302-308 is applied on one of the images (depending on the zoomfactor) for image signal processing that may include denoising,demosaicing, sharpening, scaling, etc. In step 314, the processed imageis resampled according to the transformation coefficient, the requestedZF (obtained from zoom function 124) and the output video resolution(for example 1080p). To avoid a transition point to be executed at thesame ZF, ΔZoom can change while zooming in and while zooming out. Thiswill result in hysteresis in the sensor switching point.

In more detail, for ZF range 1:Z_(switch), for ZF<Z_(switch), the Wideimage data is transferred to the ISP in step 312 and resampled in step314. For ZF range=Z_(switch):Z_(switch)+ΔZoom_(in), both sensors areoperational and the zoom image is generated from the Wide sensor. Thecolor balance is calculated for both images according to a given ROI. Inaddition, for a given ROI, registration is performed between the Wideand Tele images to output a transformation coefficient. Thetransformation coefficient is used to set an AF position. Thetransformation coefficient includes the translation between matchingpoints in the two images. This translation can be measured in a numberof pixels. Different translations will result in a different number ofpixel movements between matching points in the images. This movement canbe translated into depth and the depth can be translated into an AFposition. This enables to set the AF position by only analyzing twoimages (Wide and Tele). The result is fast focusing.

Both color balance ratios and transformation coefficient are used in theISP step. In parallel, the Wide image is processed to provide aprocessed image, followed by resampling. For ZFrange=Z_(switch)+ΔZoom_(in):Z_(max) and for Zoom factor>Z_(switch),+ΔZoom_(in), the color balance calculated previously is now applied onthe Tele image. The Tele image data is transferred to the ISP in step312 and resampled in step 314. To eliminate crossover artifacts and toenable smooth transition to the Tele image, the processed Tele image isresampled according to the transformation coefficient, the requested ZF(obtained from zoom function 124) and the output video resolution (forexample 1080p).

FIG. 4 shows the effective resolution as a function of the zoom factorfor a zoom-in case and for a zoom-out case ΔZoom_(up) is set when onezooms in, and ΔZoom_(down) is set when one zooms out. Setting ΔZoom_(up)to be different from ΔZoom_(down) will result in transition between thesensors to be performed at different zoom factor (“hysteresis”) whenzoom-in is used and when zoom-out is used. This hysteresis phenomenon inthe video mode results in smooth continuous zoom experience.

In conclusion, dual aperture optical zoom digital cameras and associatemethods disclosed herein reduce the amount of processing resources,lower frame rate requirements, reduce power consumption, remove parallaxartifacts and provide continuous focus (or provide loss of focus) whenchanging from Wide to Tele in video mode. They provide a dramaticreduction of the disparity range and avoid false registration in capturemode. They reduce image intensity differences and enable work with asingle sensor bandwidth instead of two, as in known cameras.

All patent applications mentioned in this specification are hereinincorporated in their entirety by reference into the specification, tothe same extent as if each individual patent application wasspecifically and individually indicated to be incorporated herein byreference. In addition, citation or identification of any reference inthis application shall not be construed as an admission that suchreference is available as prior art to the present disclosure.

While this disclosure has been described in terms of certain embodimentsand generally associated methods, alterations and permutations of theembodiments and methods will be apparent to those skilled in the art.The disclosure is to be understood as not limited by the specificembodiments described herein, but only by the scope of the appendedclaims.

What is claimed is:
 1. A dual-aperture zoom digital camera comprising:a) a Wide imaging section that includes a fixed focal length Wide lenswith a Wide field of view FOV_(W) and a Wide sensor, the Wide imagingsection operative to provide Wide image data of an object or scene; b) aTele imaging section that includes a fixed focal length Tele lens with aTele field of view FOV_(T) that is narrower than FOV_(W) and a Telesensor, the Tele imaging section operative to provide Tele image data ofthe object or scene; and c) a camera controller operatively coupled tothe Wide and Tele imaging sections and configured to evaluate if ano-switching criterion is fulfilled or not fulfilled, wherein at a zoomfactor (ZF) value greater than a zoom factor ZF_(T)=tangent(FOV_(Wide))/tangent (FOV_(Tele)), if the no-switching criterion isfulfilled the camera controller is further configured to output a zoomvideo output image that includes only digitally-zoomed Wide image data,and if the no-switching criterion is not fulfilled, the cameracontroller is further configured to output a zoom video output imagethat includes only transformed, digitally zoomed Tele image data.
 2. Thecamera of claim 1, wherein the ZF value expresses a maximal zoom Zmax.3. The camera of claim 1, wherein the no-switching criterion includes ashift between the Wide and Tele images calculated by globalregistration, the shift being greater than a first threshold.
 4. Thecamera of claim 1, wherein the no-switching criterion includes adisparity range calculated by global registration, the disparity rangebeing greater than a second threshold.
 5. The camera of claim 1, whereinthe no-switching criterion includes an effective resolution of the Teleimage being lower than an effective resolution of the Wide image.
 6. Thecamera of claim 1, wherein the no-switching criterion includes a numberof corresponding features in the Wide and Tele images being smaller thana third threshold.
 7. The camera of claim 1, wherein the no-switchingcriterion includes a majority of objects imaged in an overlap area ofthe Wide and Tele images being calculated to be closer to the camerathan a first threshold distance.
 8. The camera of claim 1, wherein theno-switching criterion includes some objects imaged in an overlap areaof the Wide and Tele images being calculated to be closer than a secondthreshold distance while other objects imaged in the overlap area of theWide and Tele images being calculated to be farther than a thirddistance threshold.
 9. The camera of claim 1, wherein the cameracontroller includes a user control module for receiving user inputs anda sensor control module for configuring each sensor to acquire the Wideand Tele image data based on the user inputs.
 10. The camera of claim 9,wherein the user inputs include a zoom factor, a camera mode and aregion of interest.
 11. The camera of claim 1, wherein the Tele lensincludes a ratio of total track length (TTL)/effective focal length(EFL) smaller than
 1. 12. The camera of claim 1, wherein the cameracontroller is further configured to combine in still mode, at apredefined range of ZF values, at least some of the Wide and Tele imagedata to provide a fused output image of the object or scene from aparticular point of view.
 13. A method for obtaining zoom images of anobject or scene using a dual-aperture zoom digital camera, comprising:a) configuring a camera controller to evaluate if a no-switchingcriterion is fulfilled or not fulfilled; b) if the no-switchingcriterion is fulfilled, configuring the camera controller to output at azoom factor (ZF) higher than a zoom factor ZF_(T)=tangent(FOV_(Wide))/tangent (FOV_(Tele)) a zoom video output image thatincludes only digitally-zoomed Wide image data; and c) if theno-switching criterion is not fulfilled, configuring the cameracontroller to output a zoom video output image that includes onlytransformed, digitally zoomed Tele image data.
 14. The method of claim13, wherein the ZF value expresses a maximal zoom Zmax.
 15. The methodof claim 13, wherein the no-switching criterion includes a shift betweenthe Wide and Tele images calculated by global registration, the shiftbeing greater than a first threshold.
 16. The method of claim 13,wherein the no-switching criterion includes a disparity range calculatedby global registration, the disparity range being greater than a secondthreshold.
 17. The method of claim 13, wherein the no-switchingcriterion includes an effective resolution of the Tele image being lowerthan an effective resolution of the Wide image.
 18. The method of claim13, wherein the no-switching criterion includes a number ofcorresponding features in the Wide and Tele images being smaller than athird threshold.
 19. The method of claim 13, wherein the no-switchingcriterion includes a majority of objects imaged in an overlap area ofthe Wide and Tele images being calculated to be closer to the camerathan a first threshold distance.
 20. The method of claim 13, wherein theno-switching criterion includes some objects imaged in an overlap areaof the Wide and Tele images being calculated to be closer than a secondthreshold distance while other objects imaged in the overlap area of theWide and Tele images being calculated to be farther than a thirdthreshold distance.
 21. The method of claim 13, further comprising thestep of configuring the camera controller to combine in still mode, at apredefined range of ZF values, at least some of the Wide and Tele imagedata to provide a fused output image of the object or scene from aparticular point of view.
 22. The method of claim 13, wherein the stepof configuring the camera controller to combine in still mode, at apredefined range of ZF values, at least some of the Wide and Tele imagedata to provide a fused output image includes configuring the cameracontroller to combine Wide and Tele image data only in focused areas.